A drilling tool comprising drill bits for rock drilling usually comprises a plurality of drill bits, made out of a hard material, embedded in a drilling head of relatively softer material, such as steel. The drill bits usually have a cylinder-like part that is embedded in the steel and a dome-shaped end profile that projects from the steel.
Such drill bits are usually manufactured from a composite material, constituted by a hard phase and a binder phase. The hard phase is usually tungsten carbide and the binder phase is often cobalt. Lubricant is also used to simplify the shaping of the drill bits. This composite material is compressed into a desired drill bit shape (green body) and is heated (often under controlled pressure and in a gas mixture specially adapted for the process) so that the binder phase becomes more viscous and wets the tungsten carbide particles and the tungsten carbide particles are joined together in this way. Depending on the starting material the drill bits will shrink to the desired final geometry during the cooling stage of the sintering process. They are then ground and cascaded. During the cascading the drill bits are mechanically treated as they rub against one another or against an added abrasive material. Cascading is used to get rid of corners and to round off edges on the drill bits and is considered to be the most economic method for cleaning and surface treating. In cascading, water in combination with an addition of so-called compound is usually used. The compound can be cleaning, de-greasing, pH-regulating, protective against corrosion, lubricating and grinding. In order to hold the components that are being cascaded apart, so called chips can be used. The chips are solid bodies that can have different shapes, such as pyramidal, conical, cylindrical etc.
Certain types of sintered carbide, such as composite material with a hard phase with an average particle size of circa 2.5 micrometers and with circa 6% binder phase, are fine-grained and thereby very hard. Such composite material therefore has such hardness that it is considered to be too hard and brittle to be used when drilling in hard rock, typically quartz rock. In this type of rock a softer composite material is therefore used for the drill bits, for example material having a greater average particle size in the hard phase and/or with a higher binder phase content. In these cases the drill bits unfortunately wear out much more quickly and the drilling tool has a shorter lifetime. Another example of when one has to change to a softer drill bit is when drilling in iron ore.
U.S. Pat. No. 7,258,833 discloses a method that increases the surface toughness and the surface hardness of tungsten carbide components. The authors of the patent claim that the method prevents the formation of cracks and/or the rupture of the components and increases their abrasion resistance. Furthermore, the authors of the patent claim that the method substantially increases the surface hardness of treated components.